1. The Field of the Invention
Photophobia, or light sensitivity, describes an adverse response to light that characterizes several neurologic conditions. The present invention relates to managing the effects of light on a subject. More particularly, the present invention relates to methods, systems, and apparatus for reducing the frequency and/or severity of photophobic responses or for modulating circadian cycles.
2. The Relevant Technology
The retina of the eye contains various photoreceptor cells. These photoreceptor cells include rods (which are involved in black-and-white and low light vision), cones (which are involved in daytime vision and color perception), and melanopsin ganglion cells.
The melanopsin ganglion cells are photosensitive. This photosensitivity can transmit pain through the pain pathways of the brain. These pathways are further described by Noseda et al. in A Neural Mechanism for Exacerbation of Headache by Light Nat Neurosci. 2010 February; 13(2):239-45 PMID 20062053, which is hereby incorporated by reference in its entirety. It has been demonstrated previously that modulating ambient light through the use of spectacle tints can be effective in the treatment of light-sensitive neurological conditions including migraine and benign essential blepharospasm. A description of these beneficial effects may be found in Good et al. The Use of Tinted Glasses in Childhood Migraine Headache. 1991 September; 31(8):533-6 PMID 1960058 and Blackburn et al. FL-41 Tint Improves Blink Frequency Light Sensitivity and Functional Limitations in Patients with Benign Essential Blepharospasm Ophthalmology. 2009 May; 116(5):997-1001 PMID 19410958, which are both hereby incorporated by reference in their entirety In addition to pain pathways, melanopsin ganglion cells also connect to the suprachiasmatic nucleus, where they participate in entrainment of circadian rhythms. These connections are further described by Hannibal J. Roles of PACAP-containing retinal ganglion cells in circadian timing. Int Rev Cytol. 2006; 251:1-39. Review. PubMed PMID: 16939776, which is hereby incorporated by reference in its entirety.
All animals have an intrinsic “clock” that synchronizes them with the earth's light/dark cycle of 24 hours. This clock establishes an internal rhythm of about (“circa”) one day (“dian”). This phenomenon is described by Czeisler C A, Gooley J J. Sleep and circadian rhythms in humans. Cold Spring Harb Symp Quant Biol. 2007; 72:579-97. Review. PubMed PMID: 18419318, which is hereby incorporated by reference in its entirety. However, in order to stay optimally synchronized with the dark/light cycle, the body's internal clock must be reset each day. This entrainment occurs when light in the environment is absorbed by the melanopsin ganglion cells and a signal is transmitted to that part of the brain that serves as the body's “master clock”, the suprachiasmatic nucleus, as described in Czeisler C A. The effect of light on the human circadian pacemaker. Ciba Found Symp. 1995; 183:254-90; discussion 290-302. Review. PubMed PMID: 7656689 and Duffy J F, Wright K P Jr. Entrainment of the human circadian system by light. J Biol Rhythms. 2005 August; 20(4):326-38. Review. PubMed PMID: 16077152, both of which are hereby incorporated by reference in their entireties.
Rhodopsin is the photosensitive molecule in the rods and cones of the eye. Rhodopsin has two metastable isomers including an active and an inactive state. When exposed to light, the rhodopsin isomerizes to an inactive isoform. The inactive isoform of rhodopsin can be recycled in the retinoid cycle. During the retinoid cycle, the rhodopsin leaves the photoreceptor and enters the retinal pigment epithelium. After being recycled to an active isoform, the rhodopsin returns to the photoreceptor. The melanopsin of the melanopsin ganglion cells is believed to undergo a similar process as described in Mure L S, Cornut P L, Rieux C, Drouyer E, Denis P, Gronfier C, Cooper H M. Melanopsin bistability: a fly's eye technology in the human retina. PLoS One. 2009 Jun. 24; 4(6):e5991. PubMed PMID: 19551136, which is incorporated hereby by reference in its entirety.
Therefore, it would be desirable to manage the effects of light on a subject. More particularly, it would be desirable to provide methods, systems, and apparatus for reducing the frequency and/or severity of photophobic responses. It would be also desirable to provide methods, systems, and apparatus for modulating circadian cycles.